How to calculate a centrifugal pump for a jet boat.

1. Apr 14, 2013

beef supreme

I am building a jet boat as a project this year. I am going construct the impeller my self but don't know what dimensions I need to make it to get the most out of the engines without over loading them. Here's what I have to work with:

The power source is going to be approximately 90 hp at 3600 rpm with about 130 ft-lb of torque. That power is going to be transmitted by two B section v-belts and pulleys. What I'm trying to accomplish is to get as close to 90 hp out of a water jet as possible. I can do about 50 square inches at the input and output of the impeller and a nozzle of about 12.5 square inches at the rear of the boat. My question is what diameter do I want to make the impeller assuming the circumference times the height of the opening at the edge is equal to the intake (50 inches^2) and what rpm?

Any insight on the matter would be greatly appreciated. Thanks

2. Apr 14, 2013

CWatters

I think you need to go find a jet boat forum. I suspect optimising the prop to match the boat is as much a black art as a science.

3. Apr 14, 2013

beef supreme

I really need someone who has a good general knowledge of fluid dynamics and such who can perhaps give me a formula to figure how to achieve the maximum gross thrust with the 90ish horsepower input.
People on boat forums, in my experiences, generally haven't known much about the physics surrounding these things.

4. Apr 15, 2013

cjl

Honestly, I think you'd be best off buying a premade impeller designed for about your level of power input. This is far from a trivial calculation, and as CWatters said, is probably as much a black art as it is a science (unless you have access to an advanced CFD program and a supercomputer, as well as a fair amount of time to figure out how to run it).

5. Apr 17, 2013